Method, system, and network entity for detecting a connection fault

ABSTRACT

A method, a system, and a network entity enable a detection of a connection fault and perform the switch-over in less than 50 ms. CV packets are being sent, for example, 1/10 ms (1 CV packet per 10 ms) or 1/15 ms (1 CV packet per 15 ms). The interval of the CV packets, consequently the frequency for sending CV packet, can be any interval that makes the switch-over time for a protected substantially real-time connection achievable. Moreover, the interval (the frequency) should be such that the interval makes the fault detection from the fault event to occur in less than 50 ms and triggers the switch-over to occur also in less than 50 ms from the occurrence of the fault event.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to communicating data over acommunication link.

BACKGROUND OF THE INVENTION

Ever since the formation of the global network of interconnectedcomputing devices such as the Internet, there is being a huge emergingof various communication formats enabling these computing devices tocommunicate among themselves. This has created various services forusers in business and non-business areas. In later half of 1990's we sawthe boom of the Internet. A whole set of new services and content becameavailable to the consumers during a short, revolutionary and hypeintense period. That period introduced e-commerce, Internet ServiceProviders (ISPs), Portals, eyeballs game, dotcom companies and even thenew economy.

However, many of the communication formats were originally designed fortraditional packet based transmission, where association to real timeevent typically lacked. An example of such a communication is the webpages and web surfing. Also many trusted application such as bankingcould be taken care with possible delays. Even the fastest datacommunication ways such as Asynchronous Transfer Mode (ATM) weredesigned, despite of the ultimate data transfer speed, to quite delaytolerant environments. Lately the telecommunication industry has beenhighly focused on their leap towards using IP for telecommunicationservices. As one alternative, Multiprotocol Label Switching (MPLS) canbe chosen as the bearer of IP, especially in large backbone networks.

However, the MPLS carries the heritage of delay tolerant based datacommunication such as the ATM, despite offering a fast way to transferdata. Consequently, there are still some remains of the ATM in the MPLS.One example is the principal design for applications substantially basedon non real time or alternatively expressed as delay tolerance.

Examples of such approaches have been presented according tostandardization specification drafts of the ITU-T: Y.1710 “Requirementsfor OAM functionality in MPLS networks” COM 13-14-E July 2002, Y.1711“OAM mechanism for MPLS networks” COM 13-15-E July 2002, and Y.1720“Protection Switching for MPLS networks” COM 13-R 14-E June 2001, allthree incorporated herein as a reference, where ConnectivityVerification (CV) packets are sent 1/s (1 per second). This standardsolution provides a fault detection time of three seconds from the faultevent.

Existing MPLS Path failure-detecting mechanism can inform both ends ofthe backbone about failures using the backward and forward detectindicators (BDI and FDI), although typically Label Switched Path (LSP)has a one-way character. The Connectivity Verification (CV) packetscheck the network for Path-specific errors like mis-merging or swappedPaths. A Path failure has occurred when defects on three consecutive CVpackets have been detected. This means that it takes three secondsbefore a failure alert for a Path error can be detected and sentfurther.

A disadvantage of the above-identified standards is that the solutionsaccording to the above-identified standards are not adequate for anycommunication or connections requiring real time functionality.Moreover, the switch-over time is not fast enough with substantiallyreal-time based connections, where a switch-over is typically requiredin less than 50 ms.

In view of various inherent limitations of communication and systemsbetween computing devices, it would be desirable to avoid or mitigatethese and other problems associated with prior art. Thus, there is aneed to have a fault detection and switch-over functionality for realtime application.

SUMMARY OF THE INVENTION

Now a method, a system and a network entity have been invented fordetecting a fault and performing a switch-over functionality for realtime application.

In accordance with a first aspect of the invention there is provided amethod for detecting a connection fault and accordingly performing aswitch-over in data communication in accordance with a set of rulesbased on Operation and Maintenance data communication principles,wherein an interval for sending connectivity verification datainformation in the data communication is such that a real time baseddata communication is achievable.

In accordance with a second aspect of the invention there is provided asystem for detecting a connection fault and accordingly performing aswitch-over in data communication between a source computing device anda sink computing device in accordance with a set of rules based onOperation and Maintenance data communication principles, wherein aninterval for sending connectivity verification data information in thedata communication is such that a real time based data communication isachievable.

In accordance with a third aspect of the invention, there is provided anetwork entity for detecting a connection fault and accordinglyperforming a switch-over in data communication in accordance with a setof rules based on Operation and Maintenance data communicationprinciples, the network entity comprises means for sending connectivityverification data information with a frequency in the data communicationsuch that a real time based data communication is achievable.

In accordance with the fourth aspect of the invention, there is provideda network entity for detecting a connection fault and accordinglyperforming a switch-over in data communication in accordance with a setof rules based on Operation and Maintenance data communicationprinciples, the network entity comprises means for receivingconnectivity verification data information with a frequency in the datacommunication such that a real time based data communication isachievable.

In preferred arrangement, method, system and network entity enable adetection of a connection fault and perform the switch-over in less than50 ms. The solution differs from the standard at least in such a waythat connectivity verification data information such as CV packets arebeing sent, for example, 1/10 ms (1 per 10 ms) or 1/15 ms (1 per 15 ms),which ever interval that makes the switch-over time for a protectedsubstantially real-time based connection achievable, that makes thefault detection from the fault event to occur in less than 50 ms, andtriggers the switch-over to occur also in less than 50 ms from theoccurrence of the fault event.

A benefit of the embodied invention provides a solution to achieve same(or even better) switch-over time in, for example, MPLS networks aswhich have been achieved in Time Division Multiplexing (TDM) networks.

For better understanding of the present invention reference is made tothe following description, taken in conjunction with the accompanyingdrawings, and its scope will be pointed out in the appending claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 depicts an example of an OAM function type codepoints,

FIG. 2 depicts an example of a payload structure of the CV packet,

FIG. 3 depicts an example of 1+1 protection switching architecture,

FIG. 4 depicts in a form of a flow chart a method for detecting aconnection fault and accordingly performing a switch-over in accordancewith an embodiment of the invention,

FIGS. 5 and 6 depict examples of the packet layer structure in datacommunication in accordance with the embodied invention,

FIG. 7 depicts an embodiment of a network system in which the principlesof the invention are applied.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The preferred embodiments of the invention provide a method, a system,and a network entity to enable a detection of a connection fault andperform the switch-over in less than 50 ms. The solution differs fromthe standard at least in such a way that connectivity verification datainformation such as CV packets are being sent, for example, 1/10 ms (1CV packet per 10 ms) or 1/15 ms (1 CV packet per 15 ms). The interval ofthe CV packets, consequently the frequency for sending the CV packet,can be any interval that makes the switch-over time for a protectedsubstantially real-time based connection achievable. Moreover, theinterval (the frequency) should be such that the interval makes thefault detection from the fault event to occur in less than 50 ms andtriggers the switch-over to occur also in less than 50 ms from theoccurrence of the fault event.

The appliance of the embodied invention for real time data communicationprovides also an advantage over the current Voice over IP (VOIP)solutions as the monitoring of the network traffic, which is based onthe label(s) as defined in the MPLS and Ethernet based solution, isconsiderably faster than the current solution of the VoIP.

Some embodiments of the invention apply Operation and Maintenance (OAM)data communication principles. The OAM is a technology that covers howone gets an overview of the network performance and its trafficbehavior, the networks detection of errors and how they are handled, andthe discovery of inconvenient configurations. Some more technicaldetails on the OAM can be found from the standardization specificationsdrafts of the ITU-T: Y.1710, Y.1711, and Y.1720, all three incorporatedherein as a reference.

Some embodiments of the invention apply connectivity verification datainformation. By the connectivity verification data information, it isverified that the connection exists and that the connection isappropriate between the network nodes. The Connectivity Verification(CV) packets can be applied as the connectivity verification datainformation. The CV flow is generated at the Label Switched Path's(LSP's) source Label Switched Router (LSR) with a nominal frequency of,for example, 1/10 ms (1 CV packet per 10 ms) or 1/15 ms (1 CV packet per15 ms). The interval for the CV flow generation nominal frequency can bewhich ever interval that makes the switch-over time for a protectedreal-time based connection achievable, and which interval makes thefault detection from the fault event to occur in less than 50 ms and,consequently, triggers the switch-over to occur also in less than 50 msfrom the occurrence of the fault event. The CV flow is terminated at theLSP's sink LSR. The CV packet contains a network-unique identifier suchas TTSI (Trail Termination Source Identifier) so that all types ofdefects can be detected. Alternatively, in Ethernet based solutionconnectivity verification data information can be referred by adifferent name, however, by the connectivity verification datainformation, it is verified that the connection exists and that theconnection is appropriate between the network nodes.

The connection comprises a functional connection between a Source andthe Sink in a system of interconnected computing devices in accordancewith the protection switching data communication principles. Preferably,the connection comprises fast IP based connection for various appliancessuch as web application, e-mail, file transfer, host sessions,newsgroups, directory services, network management, and file services.The examples are described in the OSI reference model. Preferably, theSource and the Sink are coupled via the optical fiber. Alternatively, acable coupling such as a copper cable coupling or a radio link couplingcan be applied as well. The switch-over takes place for the previousconnection (typically working connection), which suffers from the faultyconnection or alternatively referred to as a connection error or afailure during the data communication. The faulty connection can be aphysical or functional between the Source and the Sink and can be causedby termination of the capability of an entity to transfer user or OAM(Operation and Maintenance) information.

In the following, technical details about the OAM's & the CV'sfunctionality are provided for some embodiments of the invention.

The CV is an important operational part of the OAM, by which datacommunication and functional connection(s) between two network nodes canbe monitored relatively reliably. The OAM defect detection function isbased on the periodic transmission of CV packets from ingress to egressof an LSP. The CV packet generation rate is, for example, 1/10 ms or1/15 ms. The interval for the CV flow generation nominal frequency canbe which ever interval that makes the switch-over time for a protectedreal-time based connection achievable, and which makes the faultdetection from the fault event to occur in less than 50 ms. As aconsequence of the appropriate interval, the switch-over is triggered tooccur in less than 50 ms from the occurrence of the fault event. Each CVpacket carries a unique TTSI (Trail Termination Source Identifier),which is composed of the source LSR identifier, and the LSP identifier.An LSP enters a defect state when one of the defects noted in section 3of the daft Y.1711 occurs. All OAM packets are identified in terms of afunction type by the first octet of the OAM packet payload as depictedin the example of FIG. 1. Thus, OAM function type codepoints (100) aredepicted.

Still referring to the CV. The Connectivity Verification function isused to detect/diagnose all types of LSP connectivity defects (sourcedeither from below or within the MPLS layer networks). An example of apayload structure of the CV (200) is depicted in the FIG. 2.

In the following, technical details about CV Source and Sink Processingare provided for some embodiments of the invention.

CV source generation and CV sink processing should be considered asindependent functions. This functional decoupling allows operators theflexibility to use different degrees of LSP monitoring on a per LSPbasis, for example, between those LSPs deemed as ‘important’ and thoseLSPs deemed ‘less-important’.

CV generation can be considered as a relatively trivial function, forexample since it never varies, and is much simpler than CV sinkprocessing. Hence, CV generation could be enabled on all (or most) ofthe LSPs, but the sink processing could be decomposed into several‘degree classes’ per LSP such as:

1. No CV processing. Hence, no defect processing, no availabilitymeasurements and no network performance measurements.

2. A simple check of CV arrivals without examining the TTSI (though itis assumed the TTSI is still generated). This cannot provide totallyreliable connectivity verification since it cannot detect certaindefects, for example d-Mismerge/d-Mismatch.

3. Only a very simple check for arrival of CV packets with an unexpectedTTSI. This could be used on less important LSPs as a simple method fordetecting leakage of important LSP traffic (into the less importantLSP). However, there might be no other defect processing done (forexample dLOCV) and no availability measurements.

4. Full defect processing but no availability measurements. Note that ifavailability measurements are not being done, network performancemeasurements are also strictly not possible (since these should onlyrelate to when the LSP is in the available state).

5. Full defect processing and availability measurements. Thisalternative also allows the option of network performance measurementstoo.

In the following technical details on principles on protection switchingis provided for some embodiments of the invention.

Protection switching is a fully allocated protection mechanism that canbe used on any topology. It is fully allocated in the sense that theroute and bandwidth of the protection entity is reserved for a selectedworking entity. To be effective under all possible failures of theworking entity however, the protection entity must be known to havecomplete physical diversity over all common-failure modes. This may notalways be possible.

The MPLS PS architecture can be a 1+1 type, a 1:1 type, or 1:N type, andall can be applied in the embodied invention.

In the 1+1 architecture type, a protection entity is dedicated to eachworking entity with the working entity bridged onto the protectionentity at the source of the protected domain. The traffic on working andprotection entities is transmitted simultaneously to the sink of theprotected domain, where a selection between the working and protectionentity is made based on some predetermined criteria, such as defectindication. An example of the 1+1 architecture (300) is depicted in theFIG. 3.

In the 1:1 architecture type, a protection entity is dedicated to eachworking entity. The working traffic is transmitted either by working orprotection entity. The method for a selection between the working andprotection entities depends on the mechanism. The protection entity canbe used to carry (so-called) “extra traffic” when it is not used totransmit the working traffic.

Some more technical details on the protection switching can be foundfrom the drafted standardization specification Y.1720.

Some embodiments of the invention apply real time communication. Thereal time can be considered as a level of computer responsiveness that auser senses as sufficiently immediate or that enables the computer tokeep up with some external process (for example, to presentvisualizations of the weather as it constantly changes). The real-timeis an adjective pertaining to computers or processes that operate inreal time. The real time describes a human rather than a machine senseof time. The real time based data communication or connections arehighly relevant in telecommunication, especially when the IP applianceis used.

Some embodiments of the invention apply Multiprotocol Label Switching(MPLS). The MPLS is a standards-approved technology for speeding upnetwork traffic flow and making it easier to manage. MPLS involvessetting up a specific path for a given sequence of packets, identifiedby a label put in each packet, thus saving the time needed for a routerto look up the address to the next node to forward the packet to. MPLSis called multiprotocol because it works with the Internet Protocol(IP), Asynchronous Transport Mode (ATM), and frame relay networkprotocols. With reference to the standard model for a network (the OpenSystems Interconnection, or OSI model), MPLS allows most packets to beforwarded at the layer 2 (switching) level rather than at the layer 3(routing) level. In addition to moving traffic faster overall, MPLSmakes it easy to manage a network for quality of service (QoS). Forthese reasons, the technique is expected to be readily adopted asnetworks begin to carry more and different mixtures of traffic.

The invention can be applied in many kinds of networks (not just theMPLS) where the OAM (Operation and Maintenance) kind of mechanism isused for monitoring of connection existence. As an example, theappliance in Ethernet based communication providing very fast datatransfer. Fast Ethernet provides transmission speeds up to 100 megabitsper second and is typically used for LAN, WAN, and MAN backbone systems,supporting workstations with cards. Gigabit Ethernet provides an evenhigher level of backbone support at 1000 megabits per second (1 gigabitor 1 billion bits per second). 10-Gigabit Ethernet provides up to 10billion bits per second.

Fast Ethernet is a local area network (LAN) transmission standard thatprovides a data rate of 100 megabits per second. Alternatively, it canbe applied in wide area networks (WANs) and metropolitan area networks(MANs). Workstations with existing 10 megabit per second Ethernet cardcan be connected to a Fast Ethernet network. (The 100 megabits persecond is a shared data rate; input to each workstation is constrainedby the 10 Mbps card.)

Gigabit Ethernet, a transmission technology based on the Ethernet frameformat and protocol used in local area networks (LANs), provides a datarate of 1 billion bits per second (one gigabit). Alternatively, it canbe applied in wide area networks (WANs) and metropolitan area networks(MANs). Gigabit Ethernet is defined in the IEEE 802.3 standard and iscurrently being used as the backbone in many enterprise networks.Gigabit Ethernet is carried primarily on optical fiber (with very shortdistances possible on copper media). Existing Ethernet LANs with 10 and100 Mbps cards can feed into a Gigabit Ethernet backbone. An alternativetechnology that competes with Gigabit Ethernet is ATM.

A newer standard, 10-Gigabit Ethernet, is also becoming common.10-Gigabit Ethernet, being standardized in IEEE 802.3ae, is a developingtelecommunication technology that offers data speeds up to 10 billionbits per second. Built on the Ethernet technology used in most oftoday's local area networks (LANs), 10-Gigabit Ethernet is described asa “disruptive” technology that offers a more efficient and lessexpensive approach to moving data on backbone connections betweennetworks while also providing a consistent technology end-to-end. Usingoptical fiber, 10-Gigabit Ethernet can replace existing networks thatuse ATM switches and SONET multiplexers on an OC-48 SONET ring with asimpler network of 10-Gigabit Ethernet switches and at the same timeimprove the data rate from 2.5 Gbps to 10 Gbps. 10-Gigabit Ethernet isused to interconnect local area networks (LANs), wide area networks(WANs), and metropolitan area networks (MANs). 10-Gigabit Ethernet usesthe familiar IEEE 802.3 Ethernet media access control (MAC) protocol andits frame format and size. Like Fast Ethernet and Gigabit Ethernet,10-Gigabit Ethernet uses full-duplex transmission, which makes possiblea considerable distance range. On multimode fiber, 10-Gigabit Ethernetwill support distances up to 300 meters; on single mode fiber, it willsupport distances up to 40 kilometers. Smaller Gigabit Ethernet networkscan feed into a 10-Gigabit Ethernet network.

FIG. 4 has been described in the foregoing. In the following,corresponding reference signs have been applied to corresponding parts.FIG. 4 depicts in a form of a flow chart a method for detecting aconnection fault and accordingly performing a switch-over in accordancewith an embodiment of the invention. In step 400 there is establishedthe LSP(s) between the Source and the Sink nodes. The draftedstandardization specifications Y.1710, Y.1711, and Y.1720 provideddetails on the establishment step and on some part of the process. Instep 402 the CVs are sent with a nominal frequency. The CVs are sentfrom the Source to the Sink. The CV flow is generated at the LabelSwitched Path's (LSP's) source Label Switched Router (LSR) with anominal frequency of, for example, 1/10 ms (1 CV packet per 10 ms) or1/15 ms (1 CV packet per 15 ms). The interval for the CV flow nominalfrequency can be which ever interval that makes the switch-over time fora possibly protected real-time connection achievable. The interval forsending the CV packet (consequently the sending frequency) is such thatit makes the fault detection from the fault event to occur in less than50 ms. The interval triggers the switch-over to occur also in less than50 ms from the occurrence of the fault event. The CV flow is terminatedat the LSP's sink LSR. Thus, in step 404 the packets for the datacommunication between the Source and the Sink are received at the Sink.In step 406 the CV packets are detected among the received packets atthe Sink. Steps 404 and 406 can be quite instant or even combined. Instep 408 there is being monitored whether any CV packet(s) is missing orwrong. Every CV packet missing or wrong in the flow is registered. Instep 410 a threshold for missing/wrong CV packets is met or exceeded.Preferably, the threshold is three consecutive missing or wrong CVpackets. However, other threshold can be applied as well. If thethreshold of the step 410 is met, a connection fault is detected at theSink in step 412. Consequently, the connection fault notification can besent in the network (step 414). In the steps 408 and 410 if there are nomissing or wrong CV packet(s) or the threshold for the missing or wrongCV packets is not exceeded, for example, there are only few missing orwrong CV packets, the process returns to the step 404. The step 404 canbe considered as a readiness state for detecting any possible missing orwrong CV packet.

Still referring to the example of FIG. 4, alternatively the detectioncan take place at network Routers such as LSR Sink, which does notnecessary act as the final receiving end for the flow but can convey theflow forward. For example, the FDI is applied in this case to transferthe failure detect indication forward.

FIGS. 5 and 6 have been described in the foregoing. FIGS. 5 and 6 depictexamples of the packet layer structure in data communication inaccordance with the embodied invention. In FIG. 5 the packets indexedwith identifier 20 depicts an identifier for a segment of the LSP. Thepackets indexed with identifier 50 depict the identifier for LSP trafficstream for which the OAM is applied to, and the index 14 represents OAMinformation packets. An example of the packet layer structure of thedata communication in accordance with the embodied invention is depictedin FIG. 6. The lower layers of OSI reference model (L2, L3) are applied.

FIG. 7 depicts an embodiment of a network system in which the principlesof the invention are applied. The example of FIG. 7 applies theprotected connection, and is based on the 1+1 protection switchingarchitecture. A functional working connection (W) and a functionalprotecting connection (P) couples a node 1 with node 2 preferably viafast data transfer means. Preferably, optical fiber based data transferlines are applied. Alternatively, the cable coupling such as the coppercable coupling or the radio link coupling can be applied as well.Typically, the data transfer means establish a backbone of IP basednetwork connection. The system of FIG. 7 can operate as the largebackbone network using IP for telecommunication services, and the MPLScan be applied as the bearer for such a network. The node 1 and 2 can bea data computing device operating in a data networks such as a computerserver. The coupling of the node 1 and the node 2 is via routers 1, 2and 3, 4, which may also cross. The LSP is established between the nodesvia the routers. Data connection packets depicted in the FIG. 7 depictsthe segment id (20,30,40) for different segment of the Path, the id(50), and OAM packets (14). The CV packets constitute a part of the OAMpacket types (the CV type OAM packet). The sending of the CV packets isdescribed above referring to the example of FIG. 4 step 402. The CV flowis generated in the Node 1. Thus, the node 1 is acting as a Source LSRfor the LSP. The flow and the LSP is eventually directed to the node 2.Thus, the node 2 is acting as eventual Sink LSR for the LSP. Thetermination of the CV flow is operating at the Sink. Additionally themonitoring can take place at network Routers such as LSR Sink, whichdoes not necessary act as the final receiving end for the flow but canconvey the flow forward. For example, the FDI is applied in this case totransfer the failure detect indication forward.

The system, the network entity, and the computer program product canapply the procedures of the method described in the example of FIG. 4.Consequently, the method can operate in the example of FIG. 7.

Particular implementations and embodiments of the invention have beendescribed. It is clear to a person skilled in the art that the inventionis not restricted to details of the embodiments presented above, butthat it can be implemented in other embodiments using equivalent meanswithout deviating from the characteristics of the invention. The scopeof the invention is only restricted by the attached patent claims.Consequently, the options of implementing the invention as determined bythe claims, including the equivalents, also belong to the scope of thepresent invention.

1. A method for detecting a connection fault and accordingly performinga switch-over in data communication in accordance with a set of rulesbased on Operation and Maintenance data communication principles,characterized in that an interval for sending connectivity verificationdata information in the data communication is such that a real timebased data communication is achievable, wherein the interval makes afault detection from the connection fault in the data communication tooccur in less than 50 milliseconds.
 2. A method for detecting aconnection fault and accordingly performing a switch-over in datacommunication in accordance with a set of rules based on Operation andMaintenance data communication principles, characterized in that aninterval for sending connectivity verification data information in thedata communication is such that a real time based data communication isachievable, wherein the interval comprises approximately oneconnectivity verification packet per 10 milliseconds.
 3. A method fordetecting a connection fault and accordingly performing a switch-over indata communication in accordance with a set of rules based on Operationand Maintenance data communication principles, characterized in that aninterval for sending connectivity verification data information in thedata communication is such that a real time based data communication isachievable, wherein the interval comprises approximately oneconnectivity verification packet per 15 milliseconds.
 4. A methodaccording to claim 1, wherein the interval further triggers theswitch-over to occur in less than 50 milliseconds from an occurrence ofthe connection fault.
 5. A method according to claim 1, wherein the realtime based data communication presumes the switch-over to take place inless than 50 milliseconds from an occurrence of the connection fault. 6.A method according to claim 1, wherein the connection fault comprises apredetermined amount of consecutively missing or wrong connectivityverification packets in the data communication.
 7. A method according toclaim 1, wherein the data communication comprises at least one ofInternet Protocol, Ethernet, and MPLS for real time telecommunicationservices.
 8. A method according to claim 1, wherein the datacommunication comprises LSP based connection.
 9. A method according toclaim 1, wherein the data communication is based on a protectionswitching data communication principles.
 10. A method according to claim1, wherein Muitiprotocol Label Switching is contained as a bearer forthe data communication.
 11. A method according to claim 10, whereinMultiprotocol Label Switching operates as a backbone for IP based datacommunication.
 12. A method according to claim 1, wherein the datacommunication takes place between a source computing entity and a sinkcomputing entity.
 13. A method according to any preceding claims,wherein the connectivity verification data information comprises CVpackets.
 14. A method for detecting a connection fault and accordinglyperforming a switch-over in data communication in accordance with a setof rules based on Operation and Maintenance data communicationprinciples, characterized in that an interval for sending connectivityverification data information in the data communication is such that areal time based data communication is achievable, wherein, the intervalin which the connection fault occurs, the connection fault is detected,and the switch-over in the data communication is triggered to occur isless than 50 ms, with the connectivity verification data informationbeing in the form of connectivity verification packets being sent oneconnectivity verification packet per 15 ms.